In case of planarizing a sheet-like workpiece, e.g., a silicon wafer in conventional examples, a polishing apparatus such as a single-side polishing apparatus or a double-side polishing apparatus is used.
For example, in the single-side polishing apparatus, a polishing pad made of urethane foam or a nonwoven fabric is attached to a discoid turntable which is driven to rotate, and polishing slurry to improve polishing efficiency is flowed. Further, a wafer held on a polishing head is pressed against the polishing pad to perform polishing. The wafer can be attached to the polishing head by a wax, vacuum, or surface tension of a liquid.
Furthermore, for example, in the double-side polishing apparatus, a discoid planetary gear called a carrier is arranged between upper and lower discoid turntables having polishing pads made of urethane foam or a nonwoven fabric attached thereto respectively. A workpiece is inserted into and held in a holding hole of this planetary gear, and a sun gear and an internal gear meshing with the planetary gear are mutually rotated to bring about rotation and revolution of the planetary gear. The double-side polishing apparatus simultaneously polishes upper and lower surfaces of the wafer by the rotation, the revolution, rotation of the upper and lower turntables, and rubbing against the wafer. During the double-side polishing, to efficiently perform the polishing, the polishing slurry is supplied from a plurality of holes provided in the upper turntable.
However, in the polishing pad used in such a polishing apparatus, so-called clogging occurs. The clogging means that residues of a polished wafer, solid matters contained in the polishing slurry, or their mixtures are deposited on a surface layer of the polishing pad or accumulated in the polishing pad. The clogging degrades polishing efficiency or degrades flatness or surface quality of each polished workpiece.
It is general to perform various kinds of conditioning for different purposes to such degeneration of the polishing pad as described above. As the conditioning, for example, there is a method for jetting high-pressure water to a surface of the polishing pad from a cleaning nozzle head to eliminate the clogging. Furthermore, there is also a method for pressing a dressing head in which abrasive grains made of diamond are scattered against a surface of the polishing pad and scraping away a surface layer of the polishing pad including the clogging by friction of the abrasive grains and the polishing pad provided by rotating the turntable.
At the time of performing the conditioning for the polishing pad, the cleaning nozzle head or the dressing head often has an area which is obviously smaller than a surface used for polishing (a polishing surface) of the polishing pad. Thus, to clean or dress the entire polishing surface of the polishing pad, such a conditioning head is disposed to an arm, and the head can be moved from the outermost periphery to the innermost periphery of the turntable when the arm is linearly moved or turned (see, e.g., Patent Literature 1). Moreover, as disclosed in Patent Literature 1, when the turntable is rotated simultaneously with the movement of the head, the head can clean or dress the entire polishing surface of the polishing pad.